Quick Answer
Built-in current sensors on flight controllers use a simple shunt resistor method and typically read 10-20% off. External Hall effect sensors like the TBS Lucid 150A detect current through magnetic fields instead, delivering 1-2% accuracy. For casual flying the built-in sensor is fine, but for long-range builds where battery monitoring matters, a Hall effect sensor is worth fitting.
How Built-in Current Sensors Work
Most flight controllers measure current with an ADC (analogue-to-digital converter) reading the voltage drop across a small shunt resistor on the board. The voltage drop is proportional to the current flowing through it, and the FC firmware converts that reading into an ampere value.
The problem is that this method is sensitive to several sources of error. The traces between the power input and the shunt resistor add their own resistance, which varies with temperature. Solder joints, wire gauge, and connector quality all introduce additional voltage drops that the sensor cannot distinguish from the actual current draw. In practice, built-in sensors drift by 10-20% from the real value, sometimes more under heavy load.
For a 3-inch whoop drawing 15A peaks, being 20% off means your OSD might show 18A when the actual draw is 15A. Not ideal, but manageable. On a 7-inch long-range build pushing 60-80A at cruise, that same 20% error makes your remaining battery estimate unreliable.
How Hall Effect Sensors Work
Hall effect sensors take a completely different approach. Instead of sitting in the current path and measuring voltage drop, they detect the magnetic field generated by current flowing through a wire. Because the sensing element is not part of the circuit, there is no shunt resistance, no trace resistance to worry about, and no thermal drift from the power traces heating up.
This galvanic isolation is what makes Hall effect sensors so much more accurate. Typical accuracy sits around 1-2% across the full measurement range. The Matek Hall Current Sensor is a good example: it clamps around a battery cable and reads the magnetic field without cutting into the wire at all. Installation is straightforward, and it connects to the flight controller via a simple analogue signal wire.
Side-by-Side Comparison
| Feature | Built-in (ADC / Shunt) | External Hall Effect |
|---|---|---|
| Typical accuracy | 10-20% error | 1-2% error |
| Temperature sensitivity | High (drifts as traces heat up) | Low |
| Measurement method | Voltage drop across shunt resistor | Magnetic field detection |
| Installation | Built into the FC, nothing to wire | Extra module to mount and connect |
| Cost | Included with FC | Extra £15-30 |
| Best suited for | Whoops, indoor builds, casual flying | 7-inch LR, mapping rigs, any build where battery % matters |
When Does Each Make Sense?
For small builds like Betaflight whoops and freestyle quads, the built-in sensor is adequate. You will get a rough amp draw reading and a useable mAh counter. The error is consistent enough that the OSD numbers are directionally correct, even if they are not precise.
For 7-inch long-range builds, autonomous mapping rigs, or any setup where you genuinely need to know how much battery you have left, an external Hall effect sensor is a sensible upgrade. The improved accuracy means your mAh consumed counter is trustworthy, which in turn makes your battery percentage estimate on the OSD much more reliable. When you are flying miles out, that confidence matters.
If you are running a stack setup like the MicoAir405v2 F405 rather than an AIO board, you might not even have a built-in current sensor to begin with, which makes the decision straightforward. See our AIO vs Stack comparison for more on that trade-off.
Calibrating Current Sensors in Betaflight
Whichever sensor type you use, calibration in Betaflight follows the same basic process:
- Go to the Power & Battery tab in the Betaflight configurator.
- Set your battery cell count and pack capacity correctly.
- Enable the current meter if it is not already on.
- Connect a known current draw (a wattmeter on the battery lead works well).
- Throttle up to a steady hover current and note the reading on your wattmeter versus the Betaflight OSD.
- Adjust the Current Meter Scale value up or down until the two readings match.
Hall effect sensors need this calibration too, but because their baseline accuracy is so much better, the scale value will be closer to the default and the readings will stay consistent across different throttle positions and temperatures.
What to Buy
- TBS Lucid 150A DroneCAN Hall Effect Current Sensor — 150A rated, magnetic sensing, simple analogue output for most FCs
- Matek Systems Hall Current Sensor 150A
- MicoAir MicoAir743v2 AIO H743 — Example of an AIO with a built-in sensor for builds that do not need external measurement
FAQ
Q: Can I use a Hall effect sensor with any flight controller?
A: Yes, as long as the FC has an analogue current input pin (labelled "CUR" or "I_SENSE" on most boards). The Hall sensor outputs an analogue voltage that the FC's ADC reads, the same way it reads the built-in shunt. Some newer sensors use DroneCAN or other digital protocols, which require a compatible FC.
Q: Why is my built-in current sensor showing double the actual current?
A: This usually means the current meter scale in Betaflight is wrong. Check that your Current Meter Type is set to the correct option (typically "Virtual" or "Hardware" depending on the FC). Then calibrate with a wattmeter as described above. If the reading is wildly off even after calibration, you may have a damaged shunt resistor or a poor solder joint on the current trace.
Q: Is a Hall effect sensor worth it for a 5-inch freestyle build?
A: For most 5-inch builds the built-in sensor is adequate. You will get a reasonable mAh consumed reading for general flight awareness. A Hall effect sensor only becomes worthwhile when you rely heavily on the battery percentage for flight time decisions, which is more common on long-range builds than freestyle.